Down-Hole Fluid Typing Logs NMR/GWD/Pretests-Sampling — From Integrated Approach to Assess Fluid Compartmentalization and Trends

Emmanuel Caroli
TOTAL, Roissy CDG Cedex, France

Deep offshore exploration is now facing increasing challenging geological exploration contexts with a large variety of reservoir deposits, significantly compartmentalized with very different source rock maturation degrees. In such a context, fluid samples are not the only candidates for a precise hydrocarbon column assessment and all kind of continuous fluid based logs have to be integrated such as NMR (Nuclear Magnetic Resonance) and GWD (Gas While Drilling).

First fluid data to be acquired, the GWD is of very interesting value to identify formation fluid content and vertical evolution. Based of fluid chemistry, this data, acquired at surface, is a continuous log but of low vertical resolution and affected by all drilling events.

NMR is acquired on wireline mode and delivers continuous diffusion/T2 maps along the well. These fluid typing outputs are closely related to the physical properties of the fluid such as viscosity, Bo and GOR.

Finally, as reference absolute fluid data, the down-hole samples can deliver both chemical composition and physical properties. These are punctual and can possibly bias the fluid model if the samples were not totally representative of the entire oil column.

The objectives of this work were to :
1 - Cross-calibrate fluid compartments derivated from pressures and GWD, qualify each fluid unit, refine fluid phases, O/GUT and impregnated intervals.
2 - Elaborate a fluid clustering from well to well in order to qualify each fluid groups. Classify the different fluid units in term of fluid families encountered.
3 - In each fluid family, down hole trends are highlightened on the basis of GWD and NMR in order to estimate the impact of biodegradation, thermo-gravity and seal diffusion on fluid columns. This characterization process can also be derived into a serie of operational recommendations for sampling.

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